Just gonna start this off with obligatory "I'm the music dude, not an expert". I certainly found this an interesting time! I get a sense of a larger universe I'm just seeing a glimpse of.
Spoilers:
I did finish the game to the best of my knowledge, at least, I beat the lost soul and was sent back to the homescreen.
Gameplay: As ghostinthegame mentioned, it seemed a little inconsistent regarding where I could walk in the first area. Some trees seemed walkable when they shouldn't have been, some seemed to block me when I wouldn't have thought they could.
The section that had me running around in space mashing "z" was a bit frustrating. To be honest, I had to double check the dialogue to know what I was doing. There was clearly a lot of effort put into the dialogue, but the sheer volume of it did make it easy for me to glaze over instructions.
I think the game may have skipped the section inside the house. I was given the equation to figure out by the creatures within, I left and came back and I was suddenly in the next area? I couldn't seem to find a way to get them to repeat the equation or find a place to give my answer.
I liked the mazes, but I did find some of the bonus items in the chests a little redundant given the brevity of the game.
Story: It is very clear that you have quite the complex universe set out, possible a little much to drop in the span of an hour and a half game. I found some of the ideas interesting, but some of the dialogue seemed to be a bit incoherent to me. Maybe if these ideas were given to the player a little more slowly, they'd be a bit easier to digest. It might be my misinterpretation, but I did seem to feel some of the characters would benefit from having their speech combed over or having a set vocabulary.
Presentation: This was certainly an interesting game to look at, although some of the environments didn't seem to mesh together too well. The area between the house and the labyrinthine being of a lower resolution took me out of the atmosphere a little. I think some of your music choices could be a little better. A 4/4 rock song with a shred solo doesn't really say "horrors beyond comprehension" to me.
Creativity: This was a hell of a ride! The universe of this game is certainly something I couldn't have dreamed up in a hundred years.
Horror: I didn't really find myself having any kind of heart-racing terror reactions, but the setting is certainly eerie and the cosmic scale of the environment was pretty unsettling.
Theme: I'm not exactly sure how a lot of this is subterranean, the labyrinthine section within Erroris felt like it was underground somewhere, which I'm now seeing is what you've wrote as your justification. Fair play. You definitely check the box for mazes!
Conclusion: This was certainly a fascinating experience. A lot of this game gave me a similar very feeling to reading an obscure occult webpage. Looking forward to seeing what you come up with next!